1. Field of the Invention
The present invention relates to a cover for an air bag unit which is attached to a motor vehicle so as to house an air bag, which is inflated on a prescribed occasion.
2. Description of the Related Art
A conventional cover for an air bag unit is disclosed in the Japanese Utility Model Application (OPI) No. 44861/89 (the term "OPI" as used herein means an "unexamined published application"). The conventional cover is made of a softsynthetic resin, and includes an upper portion and a side portion. The upper portion covers an air bag, which is inflated on a prescribed occasion, and is broken when the air bag is inflated. The side portion extends downwardly from the peripheral edge of the upper portion. The cover has an insert embedded therein which includes a flexible net and a flexible reinforcing band assembly of high tensile strength.
The net includes a nearly-oblong annular side portion embedded in the side portion of the cover, upper portions embedded in the upper portion of the cover except in the breakable part of the upper portion of the cover, and coupling portions which couple the side portion of the net to the upper portion thereof. The net is embedded in the cover so that the upper portions of the net do not separate from the side portion thereof when the upper portion of the cover is broken due to inflation of the air bag.
The reinforcing band assembly includes a horizontal band secured to the side portion of the net along the entire perimeter of the side portion, and vertical bands secured to the side edge parts of the coupling portions of the net and to the horizontal band. The horizontal band is provided to prevent the side portion of the cover from expanding outward when the air bag is inflated. The vertical bands are provided to reinforce the coupling portions of the net and the side portions thereof under the coupling portions, because the coupling portions are forcefully pulled upwardly when the upper portion of the cover is broken and spreads due to the inflation of the air bag. To enhance the tensile strength of the coupling portions of the net and of the side portion thereof under the coupling portions, the vertical bands are long enough to extend down from the side edge parts of the coupling portions of the net to locations under the side portion of the net along the horizontal band and be secured at the lower ends of the vertical bands to the body of a steering wheel. Since the vertical bands, which are expensive are long, the cost of the material for the cover is high which presents a problem. In addition, the vertical bands need to be secured to the body of the steering wheel, and the area of the portions of the vertical bands which are sewn to the side portion of the net is large due to the large length of the vertical bands. Therefore, the number of manufacturing steps for the cover and the cost of manufacturing are high which is also a problem.